The drilling process for oil and gas exploration typically requires the installation of production tubing that extends from the underground oil and gas reservoir to the well surface. This production tubing serves as a conduit for the recovery of the oil and gas from the reservoir. The production tubing is typically placed in a protective pipe liner called a tubular casing. The tubular casing, in descending diameters, extends in many cases to hundreds of feet and is often cement is placed within the annulus located between the tubular casing and the well bore to hold the tubular casing in place and to ensure a pressure-tight connection between the well surface and the oil and gas reservoir.
Usually the tubular casing remains within the well bore until it has been determined that no oil or gas reservoirs have been found or the reservoirs have been exhausted. In such cases, the well bore must be plugged and abandoned (P & A) as required by law or convention. When a well bore is plugged and abandoned, the casing tubular is typically removed to a desired or prescribed depth and disposed of in a safe manner.
In other cases, an existing well bore is often utilized to allow the well to be drilled in a different direction. Often in such cases, the drill bit being used to advance the drilling cannot pass through the previously installed tubular casing due to an obstruction. If that occurs, it is necessary to remove the casing tubular to a desired depth before drilling operations can be restarted.
In most wells there are at least four tubular strings, beginning with the largest, upper and outer most conductor pipe, the surface casing, the intermediate tubular and finally the production casing. The removal of the tubular casing when required is often very difficult due to the tremendous weight of the tubular strings and, in some cases, the cement that has been placed around and between the various tubular strings.
The removal of the tubular casing from the well, such as when a well is to be plugged and abandoned, generally begins by first inspecting the well and insuring that the well is inactive and free of any residual gas and that the well is safe to allow for removal of the blowout preventers, well head, and other well equipment that is positioned above the tubing hangers. A safe work platform is then established around the wellhead and associated equipment. That work platform is then used to create a bridge plug within the production tubular at a prescribed depth by applying cement to seal or plug the well casing. The production tubular is then cut at a prescribed depth below the surface using chemical cut, jet cut, mechanical cut or other such rotating cutting tools. The cutting tool is supported on the surface and rotated by a rotary swivel. A lifting device is then attached to the inner most tubular by screwing into or spearing the tubular tubing hanger.
Such lifting devices may be the rig's crane if available and not in use by other drilling operations on the site. The production tubular is then lifted to a desired length, usually approximately forty feet, where slips are set to hold the string and tongs are used to uncouple the tubular joints. However, in many cases the drill casing tubular cannot be uncoupled in this manner. In the latter case, two diametrically opposing holes are cut in the casing and a bar is then inserted through the holes and the lifting device, such as a crane, is slaked off to allow the bar to rest on top of the well flange. The tubular is then flame cut just above the bar and the initial section of tubular is then removed. In some cases, where cement is present between the tubular strings, it becomes necessary to chip away the cement in order to cut the lifting bar holes. The crane then returns and is attached to the bar thus lifting the tubular string for another length and holes are again cut for a lifting bar. The process described above is then repeated for each tubular string until all the tubulars are removed.
Each incremental section of tubular usually requires operators to cut the casing, usually by torch, and manually drill two holes. The two holes are drilled from each side of the tubular in an attempt to keep them aligned with each other. It is essential that the holes be aligned with each other or large enough so that the bar or rod can be placed through the two holes. As discussed above, raising the tubular requires an extensive amount of force to overcome the resisting forces. Therefore, a stable platform is required. After the various increments of casing tubular are cut and pulled from the well bore, they are disposed of in a prescribed manner. Where holes drilled for the bars are individually and sequentially drilled in each incremental section of casing it is essential that proper tooling be used to maintain alignment. The operators usually drill one side at a time, a slow and tedious process, especially with heavy gauge pipe. In some cases up to two hours is required. The operator is required to drill a second hole that is diametrically opposite the first. In some cases the operator is fortunate enough to get the two holes lined up, but at other times the two holes did not line up and a bar could not be inserted through both holes in which case a torch is used to enlarge at least one of the holes so that the bar could be placed through both holes.
A dual drill system that drills holes from both sides simultaneously thereby insuring alignment may be used. Although the time required to drill the holes may be drastically reduced in such cases, a significant amount of time is still required to set up, and to clear, lubricate and repair the drill bits. In addition, a torch is still often used to cut each section of the tubular being removed. Since a torch is used to separate the tubular into reasonable lengths, it has become more prevalent to simply cut the holes with a torch as well. In view of the process described above, a faster and more efficient method is needed to perform these tasks with greater certainty.
In more recent years the P & A operation has included the use of a portable power swivel to assist in cutting casing down hole for removal. Such power swivels are generally portable hydraulic systems used on a well site having multiple well heads and where existing cranes are not always available for the P & A operation. Therefore, a temporary derrick must be erected adjacent the wellhead to be removed and the P & A operation carried out using the power swivel. Such derricks may or may not include a means for raising the well casing. In most cases a simple frame to support well casing cutting tools is sufficient to separate sections of the well casing. Such frames have evolved from a simple “A” frame structure to more complicated wellhead adapted frames having a vertical mast traversable in at least two planes.
However, in most cases the frames are fitted so as to include a power swivel and its cutting tools. However, in many cases such adaptation to an offshore wellhead is not necessary on well sites having multiple well heads. Such sites have very limited space available and therefore the size of the temporary derrick must be restricted. Therefore, a simple skid having traversable mast to support a plurality of tools is all that is needed. There a power swivel may be one of several tools that may be adapted to the mast, thereby making the skid and mast assembly much more universal.
While certain novel features of an embodiment of this invention are described below and pointed out in the drawings and annexed claims, the invention is not intended to be limited to the details specified herein, since a person of ordinary skill in the relevant art will understand that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation may be made without departing in any way from the scope of the present invention. No feature of the invention is critical or essential unless it is expressly stated as being “critical” or “essential.”